Blender NPR: flat shader that shows depth?
Fol Amor's toon shading was a combination of:

Self-luminated material (the flat-looking character)
Shadow pass (maya has ramp shaders, don't know about blender)
Rim pass (shader that highlights white around character)
zdepth as mentioned above.

it also has to do with how you composite all those passes together. You can do so via Adobe After Effects.

If you dig around vimeo, some of their artist have a making of that's specifically towards their render passes.

Their film's environment was a combination of 3d props/visuals with 2d matte paintings for the background.

Cheers!